This keyword data block is used to define pressure during batch-reaction steps. This data block can also be used to specify the pressure in a cell or range of cells during advective-transport calculations (**
ADVECTION
**
) and advective-dispersive transport calculations (TRANSPORT).

Line 0: REACTION_PRESSURE 1 Three explicit reaction pressures.

Line 1: 1.0 250.5 500.0

Line 0: **
REACTION_PRESSURE**
[*
number*
] [*
description*
]

**
REACTION_PRESSURE**
is the keyword for the data block.

*
number*
--Positive number or a range of numbers to designate this pressure definition. A range of numbers may be given in the form *
m-n*
, where *
m*
and *
n*
are positive integers, *
m*
is less than *
n*
, and the two numbers are separated by a hyphen without intervening spaces. Default is 1.

*
description*
--Optional comment that describes the pressure data.

*
list of pressures*
--A list of pressures (atm) that will be applied to batch-reaction calculations. More lines may be used to supply additional pressures. One batch-reaction calculation will be performed for each listed pressure.

Line 0: REACTION_PRESSURE 1 Three implicit reaction pressures.

Line 1: 1.0 500.0 in 3 steps

Line 0: **
REACTION_PRESSURE**
[*
number*
] [*
description*
]

Line 1: pres_{
1}
*
, *
pres_{
2}
*
,*
**
in**
*
steps*

pres_{
1}
--Pressure of first reaction step, atm.

pres_{
2}
--Pressure of final reaction step, atm.

**
in**
*
steps*
--“**
in**
” indicates that the pressure will be calculated for each of *
steps*
number of steps. The pressure at each step, *
i*
, will be calculated by the formula

; if *
steps*
= 1, then the pressure of the batch reaction will be
. Example data block 2 performs exactly the same calculations as Example data block 1. If more batch-reaction steps are defined by KINETICS, REACTION, or REACTION_TEMPERATURE input, the pressure of the additional steps will be pres_{
2}
.

If more batch-reaction steps are defined in KINETICS, REACTION, or REACTION_TEMPERATURE than pressure steps in **
REACTION_PRESSURE**
, then the final pressure will be used for all of the additional batch-reaction steps. INCREMENTAL_REACTIONS keyword has no effect on the **
REACTION_PRESSURE**
data block. The default pressure of a reaction step is equal to the pressure of the initial solution or the mixing-fraction-averaged pressure of a mixture. **
REACTION_PRESSURE**
input can be used even if there is no REACTION input. The method of calculation of pressure steps using “**
in**
” is slightly different than that for reaction steps. If *
n*
pressure steps are defined with “**
in**
*
n*
” in a **
REACTION_PRESSURE**
data block, then the pressure of the first reaction step is equal to *
pres*
_{
1}
; pressures in the remaining steps change in *
n-1*
equal increments. In contrast, if *
n*
reaction steps are defined with “**
in**
*
n*
” in a REACTION data block, then the reaction is added in *
n*
equal increments.

In an advective-transport calculation (**
ADVECTION
**
), if

The keyword **
REACTION_PRESSURE**
is used in example problem 2.

ADVECTION, KINETICS, REACTION, REACTION_TEMPERATURE, and TRANSPORT.